The present invention relates to a method of cleaning broken glass. More specifically to a method and plant for removing labels and debris from broken glass and preparing it for processing in a crusher/classifier where it is further crushed and sorted into smaller pieces or grades to be used in a variety of applications.
Typical recycling of glass has in the past, been a labor intensive industry as glass bottles of different colors are often sorted into separate areas prior to melting. When this glass is melted, labels, adhesives and other materials are generally burned away. The melted glass may then be processed and mixed with virgin glass as necessary.
A second type of glass recycling involves crushing glass into small particles. The processing of glass in this manner requires that the glass remain below a temperature of 600 degrees Fahrenheit, as the molecular structure of the glass begins to change above this temperature, rendering the glass unsuitable for crushing.
One of the primary uses for crushed glass is in abrasive blasting, which has replaced sand blasting in many areas. Sand blasting has commonly used silica sand as the abrasive element in the procedure. The use of silica sand has been banned or severely restricted in many areas. This is due to the silica dust contained in silica sand. Silica dust has been found to be one the most dangerous types of dust that a human can breath. Due to the toxicity of silica dust, it has been necessary to replace the sand in blasting with other abrasive media. It has been discovered that finely crushed or powdered glass has excellent qualities when used as an abrasive material. Current uses have included industrial blasting of steel equipment all the way to medical uses including abrasive blasting of dental fixtures such as dentures.
A second use for finely crushed or ground glass is as a filter media for potable public water supplies. Much research is currently being done using crushed glass as a filter media in place of sand which is typically used. Glass has been found to be superior to sand in filtering, and responds more favorably to back washing than sand filters. Still other uses include additives for paint and tiles, while larger pieces may be used for decorative applications such as gravel in fish tanks.
Recycled glass used for crushing has, in the past, been manually sorted, removing the bottles which have paper labels or adhesives. Typically, any glass which does not contain lead is suitable for use in the crushing process, regardless of color. During sorting and recycling many pieces are broken into quarter size pieces and smaller this type of glass, when of a uniform color, is referred to as cullet. If the crushed glass is not sorted as to color the resulting product is referred to as mixed cullet. Mixed cullet containing labels and label adhesives has, in the past, been unsuitable for crushing, as the labels could not easily be removed. Further, this glass is usually unsuitable for melting as it cannot easily be color sorted. Thus, this glass or mixed cullet has ended up as land fill material.
From this discussion it can be seen that it would be desirable to create a plant and method for cleaning dirty cullet containing labels so that it may be used for crushing and thus, recycled instead of ending up as land fill material. Further, it can be seen that it would be desirable to provide such a method that would remove labels and adhesives in a manner that would not change the molecular structure of the glass contained therein
The present invention addresses these problems by providing a large tumbling device into which broken pieces of labeled glass such as beverage bottles, or cullet, are fed. The glass is tumbled and passed through a flame which heats the cullet to a temperature well below 600 degrees Fahrenheit (the temperature at which the molecular structure of glass begins to change) but high enough to burn a large percentage of the labels from the glass. The tumbling process is repeated numerous times, ensuring that high percentage of the foreign material is removed, before the cullet passes through the entirety of the chamber and is cooled to be processed into the desired grades. The present invention also offers other advantages over the prior art and solves various problems associated therewith.